The intrapulmonary delivery of pharmaceutically active drugs is accomplished by a number of distinct methodologies. In accordance with one method, a pharmaceutically active drug is dispersed in a low boiling point propellant (a CFC or HFA) and loaded in a pressurized canister from which the drug/propellant formulation may be released by the use of a device generally known as a metered dose inhaler (MDI). Once released, the propellant evaporates and particles of the drug are inhaled by the patient. Another method involves the use of a nebulizer which uses vibration to create a mist of fine particles from a solution or suspension of a drug which mist is inhaled through the mouth and/or nose by the patient. In yet another method dry powered drug (which may be included in packets) are inhaled. These methods are hindered by significant problems relating to patient compliance and dosing as described further below.
The use of dry powders in systems presents some unique difficulties. Firstly, the dry powders are difficult to store and can be easily contaminated with water vapors causing the powders to clump together. Systems which do not include dry powders include the drug dissolved or suspended in a liquid carrier. Although there are advantages to these systems (e.g., avoiding the clumping of powder particles) these systems are also affected by moisture in the surrounding air, i.e. humidity. Specifically, such systems may use water as the carrier, i.e. a formulation comprised of a drug and water is used to create aerosolized particles. The carrier (such as the water) present in the particles evaporates after the particles are formed. However, the rate and amount of evaporation can vary if the surrounding humidity varies. The amount of evaporation effects the particle size which effects the amount of particles which reach the lung and the particular area of the lung which the particles can reach. Several aspects of the present invention are directed at eliminating the variability in particle size due to surrounding humidity.